The emergence of AIDS as a disease spread through sexual intercourse has prompted the search for new, effective, safe, and female-controlled vaginal microbicides for curbing mucosal viral transmission. Microbicides that are currently being investigated are directed mainly at preventing pregnancy as well as protection against sexually transmitted diseases. The availability of a non-spermicidal microbicide is equally important for (i) sexually active women to allow pregnancy while protecting both mother and child from HIV and; (ii) as a prophylactic antiviral agent, especially for HIV-1 serodiscordant couples before assisted reproductive technology procedures are undertaken. In a systematic effort to identify a broad-spectrum anti-HIV microbicide potentially capable of preventing the sexual transmission of HIV without affecting fertility, we have synthesized a series of phenyl phosphate derivatives of stavudine (STV/d4T) and identified stavudine-5'-(p-bromophenyl methoxyalaninyl phosphate) [Stampidine or STAMP], as the most potent broad-spectrum non-spermicidal anti-HIV agent. STAMP was 100-fold more potent than STV/d4T and 2-fold more potent than zidovudine (ZDV/AZT) against clinical HIV-1 isolates of non-B envelope subtype. STAMP inhibited the in vitro replication of genotypically and phenotypically nucleoside analog reverse transcriptase inhibitor (NRTI)-resistant and non-nucleoside (NNRTI)-resistant HIV-1 isolates at subnanomolar to low nanomolar concentrations. Orally administered STAMP exhibited significant and dose-dependent in vivo anti-HIV activity in Hu-PBL-SCID mice against a genotypically and phenotypically NRTI-resistant clinical HIV-1 isolate (BR/92/019). A single 50 mg/kg oral bolus dose or a 4-week treatment course with STAMP yielded therapeutic concentrations of STAMP >4-logs higher than its IC50 value and exhibited potent antiretroviral activity in feline immunodeficiency virus (FlV)-infected cats. STAMP therapy was not associated with any clinical or laboratory evidence of toxicity at dose levels as high as 500 mg/kg. STAMP exhibited favorable pharmacokinetic behavior in mice, dogs, and cats following oral administration of formulated GMP-grade STAMP (25-100 mg/kg/day) as hard gelatin capsules. STAMP has particular clinical utility as a non-spermicidal microbicide to prevent sexual transmission of cell-associated HIV-1 from infected semen to the female genital tract. The further development of STAMP may provide the basis for a new strategy aimed at prevention of the sexual transmission of multidrug-resistant HIV-1. The goals of this Phase I proposal are: (i) to examine the microbicidal activity of STAMP-containing gel formulation in vaginal HIV-1 infected Hu-PBL-SCID mouse; and (ii) vaginal FIV-infected cat models for sexual transmission of AIDS. Specific Aims 1 and 2 may provide the foundation for the clinical development of STAMP in Phase II studies as a safe, effective broad-spectrum anti-HIV microbicide without conception-inhibiting functions. [unreadable] [unreadable]